Surface-mounted electronic parts such as a chip capacitor and a chip inductor are usually mounted by soldering an external electrode formed in an electronic part main body, for example, to a land electrode for mounting disposed on a substrate.
As such electronic parts, an electronic part, which has an external electrode provided with a Sn plating layer or the like on the surface thereof for the purpose of improving solder wettability of the external electrode, is widely used.
However, when an electronic part having a plating layer formed on the surface thereof by plating is mounted by soldering, there is a problem that a plating solution or a cleaning solution remaining within the external electrode is exposed to a high temperature at the time of soldering to rapidly vaporize, and causes solder explosion (solder burst), and thereby a short circuit occurs between neighboring electrodes or electronic parts.
Then, in order to produce an electronic part which can solve such a problem, there is proposed, for example, a method for producing a capacitor (laminated ceramic capacitor), in which a conductor paste containing a spherical Cu powder, a flaky Cu powder and a glass powder, in which the amount of the flaky Cu powder is 2 to 33 parts by weight with respect to 100 parts by weight of the total Cu powder, and the amount of the glass powder is 6 to 10 parts by weight with respect to 100 parts by weight of the total Cu powder is applied onto a side surface of a rectangular parallelepiped-shaped laminate formed by alternately laminating a dielectric layer and an internal electrode layer, and fired/baked to form an external electrode electrically conductive to the internal electrode layer, and a plating layer is formed on the surface of the external electrode by a wet-plating method (refer to Patent Document 1).
In the case of a capacitor produced by this method, since a compact external electrode (Cu thick-film electrode) is formed, it is said that water or crystal water of Ni hardly penetrates into the external electrode in forming a Ni-plating layer or a Sn-plating layer by a wet-plating method, and for example, in the case of mounting a capacitor on a component pad electrode on a mother board, even when solder on the component pad electrode rises along a side surface of the capacitor in a reflow step, the amount of water required to be exuded from the inside of the external electrode and come into contact with high-temperature melted solder to cause vapor explosion is insufficient, and therefore solder burst toward the outside is suppressed to enable prevention of a short circuit between neighboring electronic parts (paragraph 0008 of Patent Document 1).
However, since a glass component which is more or less soluble in a plating solution is used in the Cu thick-film electrode, it is difficult to completely prevent the occurrence of solder burst with a method of optimizing (densifying) an external electrode alone.
Further, the plating solution is often intended to be improved, but dissolution of the glass component cannot be completely prevented, and it is actually impossible to completely avoid the occurrence of solder burst.
Further, when an outermost layer of the plating layer formed on the external electrode is a Sn plating layer as with the capacitor described in Examples of Patent Document 1, there is a problem that whiskers, in which crystals of Sn grow out from the surface of the plating layer, are generated, and these whiskers cause a short circuit.    Patent Document 1: Japanese Patent Laid-open Publication No. 2005-101470